In fact what you are doing, wont exactly work even if you dont feather. Since transparency is not coverage.
– joojaaSep 28 '19 at 15:01

I've tried several ways. Say, two gradient gave the same effect. I believe there is a way to simply invert first image, or substract it from plain black layer.
– MaxSep 28 '19 at 15:03

Instead of doing all that, can't you just fill an entire rectangle with the colour you want, and apply some transparency. What exactly are you trying to achieve here, and why are you doing it that way?
– Billy KerrSep 28 '19 at 16:40

Billy Kerr, I need these pictures for an animation on web. They form a rectangle and at some moment upper triangle should disappear. Now I use plain rectangle and second picture on my post, but it is not a perfect solution.
– MaxSep 28 '19 at 22:34

1 Answer
1

This won't work, because when you mix half-transparent pixels with half-transparent pixels, you're getting half transparent pixels: if two pixels have, say, 50% opacity, the resulting merge will be 75% opacity, not 100%.

The only way to avoid this but still get the feather that comes to my mind is to have your blur applied as a post-action: which might be impossible depending on the medium you want to use. Here's an example from After Effects with two blurred figures on the left and two sharp figures with the blur applied on top of them on the right: